Acoustic modal analysis and pressure transducer array measurements of flow induced acoustic resonances in tandem deep cavities

Strong acoustic coupling effect is formed in tandem deep cavities, along with inherent acoustic standing wave modes in the deep cavity structure. In particular, when the main flow passes through the tandem deep cavities, the leading-edge flow separation forms shear vortex devolution. Once the frequency locked and phase matched with the natural acoustic mode of the side cavity, the strong flow-induced acoustic resonances will be generated. In this paper, the effects of cavity spacing and Reynolds number on the flow induced acoustic resonances in tandem deep cavities flow were studied by acoustic modal finite element analysis and sensor array experimental measurement. The acoustic mode calculation was used to obtain the frequency and sound pressure spatial distribution of the standing wave mode in the deep cavities without incoming flow. The amplitude-frequency information and waveform of pressure pulsation of a series deep cavity with Reynolds number between 0.26×10⁵ ~ 2.17×10⁵ were obtained by sensor array plugged into the wall. The results show that the most intense acoustic resonance was generated when the deep cavities were arranged in half wavelength, and the sound pressure pulsation inside the cavity is in the same phase oscillation mode, which induces the anti-phase oscillation of the sound pressure in the main channel. Secondly, when the deep cavities were arranged in proximity, the intense sound pressure pulsation was in the anti-phase oscillation mode. However, there were only weak acoustic resonance and pressure pulsation in other arrangements.